ESTRO 2021 Abstract Book

S329

ESTRO 2021

Materials and Methods Treatment delivery errors which produce clinically significant changes to treatment plans yet are within or close to the specifications of the treatment delivery system, were designed. Facilities created a SABR spine plan to their local specifications based on standard instructions. Twelve versions of changes simulating the errors were introduced into these treatment plans, nine of which were within machine tolerance (Fig 1). Facilities performed PSQA on all 12 plans using their clinically implemented processes and tolerances and reported the results to the study investigators. The facilities also calculated the dose distributions of the error plans, from which the near maximum spinal cord dose (D 0.03cc,SC ) and dose to 90% of PTV (D 90,PTV ) were calculated centrally. To assess individual impact of the error plans, the changes in D 0.03cc,SC and D 90,PTV in the plan with the error versus in the original plan were evaluated.

Results Seventeen facilities from Australia, the UK and the US using six different radiation treatment planning systems and Varian and Elekta C arm linacs were included in the study. Of the twelve versions of a participant’s plan, between two and eight passed the local PSQA. Six of the error plans (from four facilities) which had caused a >10% increase in D 0.03cc,SC still passed PSQA (Fig 2). When the threshold was reduced to >5% this rose to 18 plans (seven facilities). Five plans (from four facilities) with D 90,PTV colder by >5% passed the PSQA.